Individuals who suffer degenerative disc disease, natural spine deformations, a herniated disc, spine injuries or other spine disorders may require surgery on the affected region to relieve the individual from pain and prevent further injury to the spine and nerves. Spinal surgery may involve removal of damaged joint tissue, insertion of a tissue implant and/or fixation of two or more adjacent vertebral bodies. The surgical procedure will vary depending on the nature and extent of the injury.
For patients with varying degrees of degenerative disc disease and/or nerve compression with associated lower back pain, spinal fusion surgery, or lumbar arthrodesis (“fusion”) is an effective method and commonly used to treat the degenerative disease. Fusion commonly involves distracting and/or decompressing one or more intervertebral spaces, followed by removing any associated facet joints or discs, and then joining or “fusing” two or more adjacent vertebra together. This fusion typically occurs with the assistance of an autograft or allograft bone graft. In certain operations, the fusion may also be assisted by a particular spinal implant or one or more bioactive materials.
Fusion of vertebral bodies involves fixation of two or more adjacent vertebrae. This procedure may be performed through introduction of rods or plates, and screws or other devices into a vertebral joint to join various portions of a vertebra to a corresponding portion on an adjacent vertebra. Fusion may occur in the lumbar, interbody or cervical spine region of a patient. A fusion is designed to stop and/or eliminate all motion in the spinal segment by destruction of some or all of the joints in that segment, and further utilizing bone graft material and/or rigid implantable fixation devices for securing the adjacent vertebrae. By eliminating movement, back pain and further degenerative disc disease may be reduced or avoided. Fusion requires tools for accessing the vertebrae and implanting the desired implant, bioactive material, etc. Such procedures often require introduction of additional tools to prepare a site for implantation. These tools may include drills, drill guides, debridement tools, irrigation devices, vises, clamps, cannulae, and other insertion/retraction tools.
Generally, there are five main types of lumbar fusion, including: posterior lumbar fusion (“PLF”), posterior lumbar interbody fusion (“PLIF”), anterior lumbar interbody fusion (“ALIF”), circumferential 360 fusion, and transforaminal lumbar interbody fusion (“TLIF”). A posterior approach is one that accesses the surgical site from the patient's back, and an anterior approach is one that accesses the surgical site from the patient's front or chest. There are similar approaches for fusion in the interbody or cervical spine regions.
Certain procedures are designed to achieve fixation of vertebral bodies, for example, in the cervical spine region, through an anterior cervical approach. The main risks of the anterior approach are vascular injury, injury to the superior laryngeal nerve leading to hoarseness, injury to the esophagus and spinal cord injury. Interbody bone grafts or cages have been designed to fit between the vertebrae at the intervertebral space and are often secured in position by anterior plating systems. The anterior approach has been the mainstay for treatment of the majority of cervical spine degenerative conditions, trauma or neurological compression conditions related to disk herniation. The anterior approach is extensile and allows exposure of the front part of the cervical spine from C2-T1. The limitations of this approach are that posterior-based pathology cannot be treated without fusion and that revision anterior surgery can be highly morbid because of damage to the vascular and neurological structures described. Since the esophagus is directly in front of the vertebral body involved in an anterior fusion, it is particularly vulnerable to revision anterior surgery. Unrecognized injury to the esophagus can lead to mediastinitis, which has an attendant mortality rate of 80%. The more levels the surgeon attempts to fuse together, the greater the risk for a failure to fuse or pseudoarthrosis. The risk for at least one level of a three level anterior fusion not healing is 50%.
Alternatively, a posterior approach to the cervical spine may be used to decompress the spinal canal or to allow for fusion. Posterior cervical fusions are performed in a fashion distinct from the anterior interbody technique. The process involves decorticating the facet joint and its attendant cartilage followed by application of bone graft between the leaves of the facet joint. Traditionally, posterior element wiring stabilized the motion segment. Lateral mass screws and plates or rods have supplanted this technique. Posterior approaches suffer the same disadvantages as posterior surgery in other areas of the spine with increased morbidity associated with bleeding, infection, damage to normal tissues and unsightly scars—issues which are not substantial concerns with anterior neck operations. Posterior cervical operations are much more painful than the anterior approach and in and of themselves necessitate longer hospital stays and longer postoperative recovery. The most common indication for posterior cervical approaches are failure of the anterior fusion to heal. Other disadvantages of traditional posterior cervical fusion include, for example, the increased length of the procedure, the complexity and over-engineered implants used to carry out the procedure, and the possible requirement of a second procedure to remove the implantation device.
Posterior cervical spinal fusion techniques have not kept pace with minimally invasive techniques available for the posterior lumbar spine and this has led to its underutilization, particularly in instances of patients at high risk for pseudoarthrosis—cigarette smokers, patients with multiple level fusions anteriorly or patients with hypothyroidism. The reason for this underutilization has to do with the difference in the anatomy of the neck which make application of the lumbar designs impractical and dangerous. A truly novel approach and instrumentation system is necessary in this scenario; it is not a simple matter of “miniaturizing” the lumbar designs. Posterior cervical fusion systems are maximally invasive leading to substantial perioperative morbidity. They are over-engineered in terms of strength and do not take advantage of the mechanical stability afforded by anterior instrumentation applied at the same time (or before in the instance of pseudoarthrosis). Posterior systems can be much smaller and less restrictive and still accomplish the goals of fusion. For example, simple wiring of the posterior elements in the face of an anterior pseudoarthrosis leads to successful athrodesis in 80% of cases. Unfortunately, posterior wiring has the unfortunate requirement of a formal posterior exposure with its attendant morbidity. Finally, the minimally invasive approach to the posterior cervical spine fusion needs to account for the unique anatomic concerns of the neurovascular and digestive anatomy as well as take advantage of the stability gained from the more easily performed anterior cervical fusion. These and other considerations are addressed by the present disclosure in more detail in the Summary and Detailed Description of the Preferred Embodiments, and the appended Claims.